Could Afghanistan's opium boom be over? Perhaps. According to the latest report of the United Nations Office on Drugs and Crime, opium cultivation has crashed in just one year, with prices at their lowest level since the late 1990s. "The bottom is starting to fall out of the Afghan opium market," says Antonio Maria Costa, executive director of the agency, which released its annual opium survey on Sept. 2.

The report's figures are startling. The U.N. agency's staff, made up of expatriates and Afghans, have been monitoring the country's poppy fields on the ground and from aerial surveillance cameras and they have found that farmers this year planted far fewer poppies  an estimated drop from last year of about 79,000 acres (about 32,000 hectares), or 22% of the country's entire opium crop. Afghanistan's output usually accounts for more than 90% of the world's heroin. The price that Afghan farmers get for their opium has also crashed, dropping by a third since last summer, from about $30 a pound ($70 per kilogram) to about $20 a pound ($48 a kilogram). (Read "Is the Taliban Stockpiling Opium?")

That's all good news. But there is a twist. Afghan poppy crops are now high-yield, say U.N. officials, thanks to better irrigation methods and especially good rains over the past year. While acreage devoted to the flowers fell, production of opium itself dropped only 10% in Afghanistan last year, to about 6,900 tons. Each hectare of poppies yielded about 123 lb. (56 kg) of opium  15% more than last year. (See pictures of a battle in Afghanistan's Kunar province.)

That more efficient cultivation has hardly been addressed by the NATO campaign to eradicate opium, according to the report. U.N. officials call the military campaign "a failure," because the strategy has focused on destroying poppy fields, without offering farmers an equivalent income if they opt to grow other crops. Fewer than 25,000 acres (10,000 hectares) have been eradicated  accounting for less than 4% of Afghanistan's opium crop. Despite that small result, Costa says the military campaign has made Afghanistan's farmers far more secretive, further complicating international efforts. "Before, opium stocks were in shacks and warehouses," he says. "Now they are underground, and not as visible." (See pictures of the hunt for Afghanistan's archeological treasures.)

Still, the U.N. report says, many Afghan farmers have apparently chosen to switch out of opium. The reasons might lie in simple market factors of supply and demand. In the years immediately following the Taliban's ouster in 2001, Afghan farmers, who had languished under a temporary Taliban ban against growing poppies, produced huge bumper crops. Those were harvested just as drug users in Europe, opium's biggest market, began to shun heroin in favor of cocaine and synthetic drugs like ecstasy. "There is definitely an issue of stocks over consumption," Costa says. "Starting in about 2006 Afghanistan has been producing a lot more opium than the world can digest."

That glut, however, could spell disaster down the road. U.N. drug officials estimate about 10,000 tons of opium have been unaccounted for since 2006 (the figure was about 8,000 tons a year ago). Costa believes the Taliban and drug traffickers in the region have stockpiled the drugs, fearing a crash in world prices if they sold the opium surplus. But the stockpiles could hugely complicate NATO's efforts to eradicate opium in Afghanistan and persuade farmers to grow other crops. That's because while some farmers seem to have switched their production, plenty of opium lies stored, potentially giving the Taliban and drug traffickers the ability to buy off officials with huge sums. Says Costa: "Opium is poisoning the society. It is corrupting leaders, politicians, members of parliament and police."